The purpose of this research is to study the mechanism by which macrophage migration inhibitory factor (MIF), derived from culture supernatants of lymphocytes stimulated by specific antigen or concanavalin A, inhibits macrophage migration in vitro. This includes the following objectives: 1. To study the effect of MIF on the metabolism of cyclic adenosine monophosphate (cyclic AMP) in purified macrophages. 2. To examine the influence of agents and drugs, modifying cyclic AMP levels, on the effect of MIF on macrophages. 3. To study the involvement of microtubules in the action mechanism of MIF. 4. To characterize and isolate the receptor for MIF present on macrophages. 5. To examine the effect of MIF on specific macrophage membrane functions. 6. To determine whether MIF acts directly on macrophages or by the intermediary of an extracellular profactor.